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Happy Pi Day Everyone!

Wednesday, March 14, 2012

It's here again, Pi Day! This is second only to May the 4th as the most important holiday on the geek calendar which includes such important days as Talk Like Pirate Day, Tweed Day, Mole Day and of course, April Fool's Day. This is not only a day to bake pies, browse dorky tshirts and calculate the circumference of your cereal bowls, it is also important to sing Happy Birthday to Albert Einstein who would be turning 133 today. I hope he was never one of the unfortunate children that got the dreaded "Pi day/Birthday" present instead of a present for each. Part of me would like to celebrate today by giving you a fantastic cherry pie recipe, but instead I'll give you a brief history of Pi and why we care about it enough to celebrate it.

Pi is a mathematical constant. Most people know this, it means pi is pi and not changing. Not ever. Every time you take the circumference of a circle and divide it by its diameter it will be pi. Personally I think that's pretty darn cool. No matter what type of circle I draw, no matter how large, how small, if I draw it with markers or in a crop field, I always know how its diameter relates to it circumference.

The idea that there was some ratio between a circle's diameter and circumference dates back farther than anyone can remember. The earliest recorded value for pi can be found in an Egyptian mathematical record, the Rhind Papyrus which was created around 1650 B.C. and gives a value for pi of 3.16. A rough estimate of pi can even be found in the Bible in I Kings 7, 23. By rough estimate I mean it gives a value of exactly 3. I will refrain from making a biblical inerrancy comment.

After the Egyptians first attempts, Archemeaies (287-212 BC) stopped trying to find the value by measuring circles and started trying to theoretically calculate pi. He thought about what would happen if you inscribed a circle between two regular polygones. What if the number of sides of those polygones kept increasing? Using this idea he found the value of pi to be 3.14185. But not only did he get a pretty good value for pi, he was also the first to say it was an irrational number. Before him, people assumed there was an exact value for pi but it turns out that though we can get very, very close with long approximations, it can never be exactly determined.

With the advent of computers, it is possible to get about as precises a value of pi as you have time for. I know many of you out there either can or know someone who can recite pi to some ridiculous number of digits. But when they start doing their little party trick, tell them to stop after the 39th digit. If you wanted create a circle that could inclose the entire universe and make it accurately enough that not even a hydrogen atom could possibly be left out, you would only need 39 digits of pi. Awesome.

I hope you all are finding your own ways to celebrate this fantastically mathematical day. I, for one, am headed home to make a cherry pi. If you would like to do the same, here's the recipe, I couldn't resist:

For Crust (Meera's Recipe – makes three crusts, keep one in the freezer)

2.5 C flour

1 tsp salt

2 T sugar

12 T butter (straight from the fridge and cut into approx 1 T chunks)

8 T chiled shortening (from a can, measure out and then chill in fridge, if using sticks, chill stick, then cut into 1 T chunks)

6 - 8 T ice water (I put ice cubes in a bowl with water, and then measure the water out from there)

For Filling

2 cans (14.5oz) pitted red tart cherries, drained

1 cup granulated sugar

¼ tsp almond extract

3-4 T quick-cooking tapioca

2 tsp unsalted butter , cut into small pieces

In a food processor with the regular blade, pulse the flour, salt and sugar to combine. Distribute the butter chunks on top of flour and pulse approx 5 1-second pulses (mixture should be pale yellow and course). Distribute chunks of shortening in the bowl and pulse about 4 more 1-second pulses.

Turn mixture into a mixing bowl. Sprinkle 6 T of water over the mixture and stir with a fork. Add more water as needed, crust should just begin to stick together, still be a little crumbly and not be wet. Divide dough and form into three disks, about 4 inches across and 1 inch tall. Refrigerate for 30 minutes.

While crust is chilling, combine sugar and tapioca, then stir in cherries and almond extract. Let that sit on the counter for 15-20 minutes.

Roll out two of the disks of dough. I roll out the crusts between pieces of plastic wrap to keep them from getting holes, and to make cleanup easier.

Line pie plate with one crust, fill as instructed for filling recipe, top with second crust, cutting vents to allow steam to escape, and crimp edges closed.

Bake at 400 F for 30 min, until top is golden. Reduce heat to 350 F baking until filling boils. Loosely cover the top with foil if needed to keep it from getting too brown. Don't forget to put a cookie sheet under your pie unless you like cleaning ovens!